1. Field of the Invention
The present invention generally relates to a patient interface device for use in a pressure support system that supplies a flow of gas to the airway of a patient, and, in particular, to a patient interface device that includes a cushion with pockets of a low-viscosity medium disposed adjacent a patient's face.
2. Description of the Related Art
There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas non-invasively to the airway of a patient, i.e., without intubating the patient or surgically inserting a tracheal tube in their esophagus. For example, it is known to ventilate a patient using a technique known as non-invasive ventilation (NIV). It is also known to deliver continuous positive airway pressure (CPAP) or variable airway pressure, such as a bi-level pressure that varies with the patient's respiratory cycle or an auto-titrating pressure that varies with the monitored condition of the patient. Typical pressure support therapies are provided to treat a medical disorder, such as sleep apnea syndrome, in particular, obstructive sleep apnea (OSA), chronic obstructive pulmonary disease (COPD), or congestive heart failure (CHF).
Non-invasive ventilation and pressure support therapies involve the placement of a patient interface device, which is typically a nasal or nasal/oral mask, on the face of a patient to interface the ventilator or pressure support system with the airway of the patient so that a flow of breathing gas can be delivered from the pressure/flow generating device to the airway of the patient. It is known to maintain such masks on the face of a patient by a headgear having upper and lower straps, each having opposite ends threaded through connecting elements provided on the opposite sides and top of a mask.
Typically patient interface devices include a mask having a faceplate and a cushion. The cushion is coupled to the faceplate. The cushion contacts the surface of the patient. The mask faceplate and cushion are held in place by a headgear that wraps around the head of the patient. The mask and headgear form the patient interface assembly. A typical headgear includes flexible, adjustable straps that extend from the mask to attach the mask to the patient.
Because such masks are typically worn for an extended period of time, a variety of concerns must be taken into consideration. For example, in providing CPAP to treat OSA, the patient normally wears the patient interface device all night long while he or she sleeps. One concern in such a situation is that the patient interface device is as comfortable as possible, otherwise the patient may avoid wearing the interface device, defeating the purpose of the prescribed pressure support therapy. It is also important that the interface device provide a tight enough seal against a patient's face without discomfort. A problem arises in that in order for the mask to maintain a seal without any undue gas leaks around the periphery of the mask, the mask may be compressed against the patient's face. Over time, the patient's face may become irritated at the point of contact between the cushion and the patient's face.
More specifically, movement, even slight movements, by the patient cause the cushion to rub against the patient's face. That is, shear forces transferred through the mask may cause the inner surface of the cushion to irritate the patient's face. Such irritation may cause red marks to appear on the patient's face. After the mask is removed, the red marks may last minutes or hours. This is a problem as patients do not like having an irritated face nor having red marks on their face.